1. Field of the Invention
This invention pertains to a hard elastic plastic retaining element for detachable fastening onto a plastic bolt provided with longitudinal ribs parallel to the bolt axis.
2. Reference to Related Art
A fastening system for fastening on a longitudinally ribbed plastic bolt is known, for example, from EP 0 697 532 B1. In the ""532 reference, a cylindrical sleeve, which may be slipped on a bolt, has several sharp-edged inward-projecting blades formed one above the other on every other quarter of the circumference of the inner wall of said cylindrical sleeve. The intermediate regions of the inner wall are smooth. To secure the fastening system, the sleeve must be turned 90xc2x0 after being slipped onto the bolt. The sharp edges of the blades then dig into the projections of the bolt ribs and provide a secure connection.
On one hand, this fastening system is somewhat expensive to manufacture due to the discontinuous blades and longitudinal ribs. On the other hand, this system is unsatisfactory in terms of assembly cost, since the sleeve must be aligned with the bolt before being slipped on and must be turned so that the blades of the sleeve go down the smooth regions of the bolt. Furthermore, after being slipped on the bolt, the sleeve must again be turned to engage the blades of the sleeve with the longitudinal ribs of the bolt.
The purpose of the invention is to configure a retaining element that it is easier to manipulate and more economical to manufacture. This problem is solved, according to the invention, by a fastener having a receiver cage featuring an inner wall which may be placed against a ribbed bolt. The fastener also includes a retaining arm formed as a springy part of the receiver cage on the side opposite the inner wall, and projecting diagonally up into the cage interior counter to the direction in which the arm may be depressed to secure the fastener. The free end of the retaining arm is provided with a sharp-cornered retaining edge. The retaining arm is directed toward the opposite wall at an obtuse angle, with the clearance of the retaining edge from the inner wall, when unstressed, being less than the outer diameter of the ribbed bolt.
As the receiver cage is pressed onto a bolt the retain arm initially bends such that the retaining edge may slide downward along the ribs. When the cage comes to rest against the base plate of the bolt, the retaining edge will dig into the ribs according to the restoring force of the retaining arm. The stronger this digging action becomes, the greater the retaining force or tensile force counter to the direction in which the retainer is pressed on the bolt.
In order to prevent a retaining edge from digging into the longitudinal ribs too strongly, a support lug, which rests against the longitudinal ribs, is provided above the retaining edge. The retaining force may be increased further by means of an additional characteristic of the invention whereby at least one sharp-cornered rib, directed into the interior of the cage, is formed on the inner wall bearing against the bolt, transverse to the longitudinal ribs.
In order to release a retaining arm, an unlatching tab is formed on the top of the arm, opposite to the direction the retainer is pressed down. The unlatching tab may be pressed against the wall of the cage, through a corresponding opening in the cage, causing the retaining edge to disengage from the longitudinal ribs and free the cage so that it may be pulled off.